If you stay in a relationship that is not healthy for you, the other family members (including the child can be affected by that) Some kids are better when they grow up in healthier, peaceful environment versus one that has tension and lacks affection.
Depending on the child's age see what would be the pros and cons if you are to stay in the relationship. If you need to, see about working with a personal coach to let you sort some of your concerns out.
Should I Stay Or Go? : How Controlled Separation (CS) Can Save Your Marriage by Lee Raffel (Paperback - Sep 1, 1999)
Imperfect Harmony: How to Stay Married for the Sake of Your Children and Still Be Happy by XXXXX XXXXX (Hardcover - Jul 29, 2003)